Question: I’ve been inspecting my sailboat to put together a spring maintenance work list. When I look closely at some of the end fittings on my stainless steel stays I see evidence of rust. First of all, since this is stainless steel, what’s up with that? But more importantly, does this rust indicate anything potentially dangerous with my rigging?
Answer: Good news and bad news here; first the good news. Your mast is still standing upright. The bad news is that the photo shows very strong evidence of crevice corrosion.
First let me explain the science. Stainless steel is only going to become stainless in the presence of oxygen, which helps to form an invisible, but highly protective oxide coating on the surface of the metal. That is what prevents rust from forming.
The photo you’ve sent shows an exposed end fitting. Sea spray and even rainwater can and will migrate down along the strands of the wire rope into the center of the end fitting, where it sits, somewhat deprived of oxygen. This in turn makes the wire rope strands vulnerable because the needed oxide coating cannot form, and the net result is that the fitting rusts from the inside out. This stay (and any wire rope fitting that looks similar) should be removed and taken to a rigging shop for further inspection. Odds are that a new piece of wire rope is going to be required—and probably a new barrel assembly as well.
Ignoring this and simply using a rust remover to clean up the surface rust you see in the photo could ultimately be the cause of the fitting breaking under load, which could lead to the mast on your boat falling down!